Process for catalytic cracking of hydrocarbons



Jan. 28, 1947. E. F. NELsoN 2,414,973

PRocEss Fon oATALYTIc cRAcxING oF Hybnocmons rFilm1 July'sl, 194s Patented Jan. 28, 1947 PROCESS FOR CATALYTIC CRACKING OF HYDROCARBONS dwin F. Nelson, Chicago, Ill., asslgnor to Universal Oil Products Company, Chicago', Ill., a corporation of Delaware Application-July 31, 1943, Serial No. 496,853

This invention relates'to an improvement in the catalytic cracking of hydrocarbon oil into gasolinefractions of high antiknock value. While the present invention is particularly directed to the cracking of oil heavier than gasoline, it is also applicable to .the treatment of a hydrocarbon fraction boiling substantially within the range of gasoline in order to improve its -antiknock characteristics.

alysts, such as acid-treated clays, may also be.

used but not necessarily with equivalent results.

During the cracking reaction, the catalyst'becomes inactivated due to the deposition thereon of a hydrocarbonaceous deposit. The exact cause Claims. (Cl. 196-52) line, and which contains constituents which form excess deposits on the catalyst, is subjected to pretreatment with a minor portion of the fresh or regenerated cracking catalyst. It is believed, although the invention is not necessarily limited thereto, .that some of these .undesirable constituents which are removed in the pretreatment step of the process comprise compounds containing nitrogen, sulfur and probably oxygen. It is also likely that highly reactive hydrocarbon compounds are also removed at least in part in the pretreating step of the present process.

It is a particular feature of the present invention that the pretreatment of .the charging oil is eected in the presence of fresh or regenerated catalyst. Thus, a relatively small amount of catalyst is usually suiiicient to remove a major portion of the deleterious components from the for the deposit on the catalyst is not definitely l known buty is believed to be due to certain undesirable constituents contained in the charging oil, aswell as being due to the cracking reaction.

T he present invention is directed to an improvey ment whereby the charging stock is subjected to a pretreatment in order toremove the undesirable constituents which form excessive deposits on the catalyst.

' In a broad aspect, the present invention relates to the cracking. of hydrocarbon oil into gasoline fractions of high antiknock value which comprises pretreating the charging oil with a portion of .the cracking catalyst and then crack'- ing the pretreated charging oil in the presence of another portion of the cracking catalyst.

In one specific embodiment, vthe present invention comprises contacting a charging oil heavier than gasoline with a minor portion of fresh or regenerated cracking catalyst, separating the charging oil, thereby providing a clean charging oil for cracking in the presence of a major portion of the fresh or regenerated catalyst, with the resulting production of an unexpected high yield of gasoline without any substantial increase in carbon deposition on the catalyst. In this way,

a relatively small amount of the catalyst is contaminated by the undesirable constituents of the charging oil and may readily be regenerated and reused, while a maior portion o! the active cat- 'alyst is utilized to convert a. clean charging oil.

The exact amount of catalystto be used in the pretreating step of the process will depend upon l the extent of impurities contained in the charging oil. In any event. this amount of catalyst will be a. minor amount of the freshly regenerated catalyst `and generally'will be less than 30% thereof and in some case itsmay be as low as 5 to 10%.

The process of the present-invention may be practiced vin any suitable manner. Although it is applicable to the treatment of hydrocarbons in the so-called fixed bed type of operation, as well as the so-'called slurry type of operation, it

' is particularly applicable to the process now catalyst from the pretreated oil and regenerating the former, and subjecting the pretreated charging oil .to cracking in the presence of a major portion of the fresh or regenerated cracking catalyst.

In accordance with the present invention, the charging oil, which is usually heavier than gasoknown in' the art as iiuidized operation.

The invention will be described in connection with the accompanying flow diagrammatic drawing which illustrates one .embodiment of the invention utilizing the iluidized operation, although it is understood that the broad scope of the present invention is not limited to this particular type of operation.

Referring to the drawing, the charging oil is introduced to the process through line I containing valve 2 into the lower portion of pretreating zone 3, wherein it is contacted with a 3 minor portion of the regenerated cracking catalyst supplied through line 4 containing valve 5. The charging stock is preheated, prior to its introduction into line I to any desired temperature, which temperature will depend upon the extent of impurities in the charging oil. In one embodiment in the invention the charging oil may be heated to substantially the same temperature as that utilized in the cracking step of the process or in another embodiment, it may be` preheated to a somewhat lower temperature of, for example,

from about 500 to about 800 F.

In pretreating zone 3, the charging oil and catalyst are passed therethrough at the desired temperature and under conditions to maintain the mixture in constant agitation. The puriied charging oil passes through line 6 in the upper portion of zone 3 into catalyst separator 'I wherein the catalyst is separated from the oil. The catalyst drops back into the upper portion of the reactor through line 8 and the spent catalyst is removed therefrom through line 9 for regeneration in a manner to be hereinafter described in detail.

The purified hydrocarbon charging oil is withdrawn from the upper portion ofzone 3 through line I0, whereafter it is commingled with a major portion of the fresh or reactivated catalyst introducedthrough standpipe II and valve I2. The mixture is then directed through line I3 into reactor I4. In reactor I4 a turbulent mass of catalyst powder is maintained in constant agitation by the rising stream of the charging oil and of the conversion products formed during the reaction. The top of this turbulent bed is illustrated diagrammatically by line I The temperature maintained in reactor I4 will ordinarily be within the approximate range of 800 to l200 F. and more generally within the range of 850 to 1000 F. The pressure in this zone will ordinarily be above atmospheric and may be of the order of 5 to 25 pounds per square inch although in some cases pressure as high as 100 pounds per square inch or more may be employed.

vaporous conversion products are withdrawn from the top of reactor I4 through line I6 into catalyst separator I1 wherein entrained catalyst is separated from the vaporous conversion proclucts and is returned through line I8 to the reactor. The hydrocarbon conversion products are then withdrawn through line I9 and valve 20 to conventional fractionating, condensing and co1- lecting means not illustrated in the drawing in 'the interest of simplicity.

The spent catalyst in reactor I4 is withdrawn therefrom through standpipe 2I wherein the catalyst is stripped of volatile hydrocarbons absorbed therein by an upwardly-moving stream of gas, such as steam, flue gas, etc., introduced through line 22 andvalve 23. This gas not only serves to strip volatile hydrocarbons from the catalyst but also serves to maintain the powdered catalyst in a fluidized state. The stripped'spent catalyst is supplied through valve 24 and is picked up by a stream of air or other suitable oxidizing gas introduced through line 25 and valve 26, and the mixture is then directed through line 21.

The'spent catalyst froml pretreating zone 3 is withdrawn therefrom through line 9 as-heretofore described and is likewise stripped of volatile hydrocarbons by means of a suitable gas introduced through line 28 and valve 29 into line 9. The spent catalyst then p'asses through valve 30 into line 21 wherein it is conveyed, along with the spent catalyst from reactor I4, into regenerator In regenerator 3I, the spent catalyst is sub-i jected to treatment in order to remove the hydrocarbonaceous deposit from the catalyst by means of a combustion reaction. In the regenerator, as in the reactor, a turbulent bed of powdered catalyst is maintained Iby an upwardlyiiowing stream of oxygen-containing gas. The upper limit of this bed is illustrated diagrammatically by line 32. Above this point the concentration of the catalyst steadily diminishes while below this point a high concentration of catalyst is maintained. Spent reactivated gases are withdrawn from the regenerator through line 33 into catalyst separator 34y wherein the entrained catalyst is thrown out by the centrifugal action and is returned to the catalyst bed by way of line 35. Vent regenerating gases are re- 4moved through line 36 and valve 31 to conventional treatment or disposal, not illustrated.

The regenerated catalyst is withdrawn from regenerator 3| by way of standpipe II and,l in accordance with the present invention, a minor portion thereof is directed through line 4 wherein it is stripped by means of a suitable gas introduced through line 38 and valve 39 and then is directed into pretreating zone 3 in the manner heretofore described, vwhile a major portion of the regenerated catalyst is directed through standpipe II and likewise is stripped by a suitable gas introduced through line 40 and valve 4I and then the catalyst is directed through valve I2 and conveyed by means of the pretreated charging oil through line I3 into reactor I5 in the manner hereinbefore described.

In an operation such as heretofore described, the yields of gasoline of high antiknock value produced from gas oil, on a once through basis, may be increased to an average of 40 to 45% by Weight of the gas oil when cracking in the presence of a silica-alumina catalyst, as compared to an average of 35 to 40% usually obtained in an operation in which the charging oil is not so pretreated. As heretofore mentioned, in spite of the increased yield of gasoline, the carbonaceous deposit on the catalyst in the reaction zone is substantially the same in'an operation utilizing the features of the present invention as in one in which the pretreatment step is not employed. The insuiiiciently converted products separated from the gasoline in the fractionating step of the process may be recycled to the reaction zone for further conversion therein.

I claimasmy invention:

1. In a catalytic cracking process, the improvement which comprises treating a hydrocarbon oil heavier than gasoline with a minor portion of a regenerated cracking catalyst at a temperature within the range of about 800 to about 1200 F. to remove deleterious carbon forming compounds from said oil without effecting anysubstantial conversion of said oil to lower boiling hydrocarbons, separating the catalyst from the pretreated charging oil, subjecting the latter to cracking in the presence of a major portion of the regenerated cracking catalyst at a temperature within the range of from about `800 to about 1200 F., withdrawing the spent catalyst from the pretreating and cracking zones and subjecting the same to regeneration, and supplying the regenerated catalyst in minor and major portions as aforesaid.

2. In a catalytic cracking process, the improveoil heavier than gasoline with a minor portion of a regenerated cracking catalyst at a temperature Within the range of about 500" to about 800- F. to remove deleterious carbon vforming compounds from said oil without effecting any substantial conversion of said oil to lower boiling hydrocarbons, separating the catalyst from the pretreated charging oil, subjecting the latter to cracking in the presence of a major portion of the regenerated cracking catalyst at a temperature within the range of from about 800 to about 1200 F., withdrawing the spent catalyst from the pretreating and cracking zones and subjecting the same to regeneration, and supplying the regenerated catalyst in minor and major portions as aforesaid.

3. In a catalytic conversion process, the improvement which comprises utilizing the charging oil to convey a minor portion of a regenerated cracking catalyst intova pretreating zone, wherein undesirable constituents Yare removed from the charging` oil without any substantial conversion of the latter to lower boiling products, separating the spent catalyst from the charging oil, utilizing the separated charging oil to con- Vey a major portion of the regenerated cracking catalyst into a cracking reaction zone operated at a temperature of from about 800 to about 1200 F. and under conditions such that the net upward flow of hydrocarbons is greater than that of the catalyst, separating the hydrocarbon conversion products from the catalyst, withdrawing the spent catalyst from the cracking reaction zone and from the pretreating zone and convey- -ing the same by means of an oxygen-containing gas to a regenerating zone in which the spent catalyst undergoes regeneration in commingled state, withdrawing the regenerated catalyst from the regenerating zone and supplying minor and major portions thereof as aforesaid.

4. In the catalytic cracking of hydrocarbon oil wherein used catalyst from the cracking step is regenerated, the method which comprises pretreating the charging oil with a minor portion of the regenerated catalyst to remove deleterious components of the charging oil Without effecting any substantial conversion of said oil to lower boiling hydrocarbons, separating the thus treated oil from said portion of the catalyst and returning the latter to the regenerating step, cracking .the separated oil in the presence of a major portion of said regenerated catalyst, and supplying used catalyst from the cracking step to the re-1 generating step. i

5. The method as defined in claim 4 furthe characterized in that the charging oil is pre.. treated with the first-mentioned portion of the catalyst at a temperature in the approximate range 0f 800-1200 F.

EDWIN F. NELSON. 

